Light and electron microscopic study of stress-shielding effects on rat patellar tendon

Abstract

In this second part of our study, the histomorphologic changes occurring in the patellar tendon (PT) of rats after sole stress-shielding were evaluated. In seven adult albino rats, both PTs were exposed by straight skin incision and then stress-shielded on one side by a cerclage, while the contralateral PT served as the sham-operated control. One animal died after the operation and was used as a negative control. After 10 weeks of otherwise unrestricted motion, the rats were killed, and the histomorphology of all PT specimen pairs compared by light and transmission electron microscopy. Light microscopy showed mid-portion thickening and irregularity of collagen bundles in the stress-shielded tendons. Intense remodelling was demonstrated by increased cellularity and vascularity, as well as by enrichment in acidic proteoglycans. Ultrastructural evaluation and morphometry revealed a predominance of large diameter (peak between 180 and 260 nm) collagen fibrils in the sham-operated controls, while in the stress-shielded tendons the number of apparently new, small-diameter (peak between 40 and 60 nm) collagen fibrils increased (up to 77% per cross-sectional field of view). The difference in peak diameters was statistically significant (p < 0.0005). This rat model demonstrated that sole stress-shielding not only causes biomechanical alterations, but also intense tissue remodelling and significant morphological changes in the collagen fibrils in the patellar tendon, comparable to so-called 'ligamentization' in experimental and clinical patellar tendon grafts for anterior cruciate ligament reconstruction.

Vaginal degeneration following implantation of synthetic mesh with increased stiffness

“…The sulphated GAG including chondroitin sulphate, heparin sulphate and dermatan sulphate are important macromolecules in the extracellular matrix, reacting quickly to tissue injury, tissue growth and changes of mechanical stimulation. GAG content increases in healing tissues, in tissue under constant compressive force and in response to stress‐shielding . The data in this study support these findings.…”

Lower strength of the human posterior patellar tendon seems unrelated to mature collagen cross-linking and fibril morphology

“…The present data show a tendency toward decreased fibril diameters in the posterior fascicles compared with the AF (Fig. 3), which suggests that the fibrils of the posterior tendon region may be relatively stress shielded (27). Since the similar concentration of PENT in the two regions indicates equivalent remodeling, the tendency toward smaller posterior fibril diameter likely reflects a congenitally moderated functional adaptation.…”

Ultrastructural Collagen Fibril Alterations in the Patellar Tendon 6 Years after Harvesting Its Central Third

“…On the other hand, predominantly small fibril sizes have been found in rats after mechanical stress shielding of the patellar tendon. 15,17 Therefore, we speculate that if the load in a tendon is altered, either increased or decreased, or if parts of it are removed, as was the case in the present study, for some reason, small-sized fibrils will develop.…”